Process for treating woven glass cloth

ABSTRACT

A solvent wash employing a polar washing solvent is employed to effectively remove the sizing agent on a woven glass cloth, while retaining the tensile strength of the woven glass cloth. Loss of tensile strength of the woven glass cloth due to removal of a sizing agent from the woven glass cloth is compensated by simultaneous or subsequent deposition of a coupling agent on surfaces from which the sizing agent is removed. The concurrent removal of the sizing agent and deposition of the coupling agent provides an effective removal of the sizing agent while maintaining sufficient tensile strength to structurally support the woven glass cloth. Further, integration of the removal of the sizing agent and the simultaneous deposition of the coupling agent in the washing solvent in a same processing step can provide a cost-effective manufacturing method for forming a finished woven glass cloth.

BACKGROUND

The present disclosure generally relates to a manufacturing process, andparticularly to a manufacturing process to clean a woven glass cloth.

“Glass cloth,” or “woven glass cloth” is a woven material that includesglass fibers. Glass cloth can be woven in various ways resulting indifferent patterns, for example, checked glass cloths for a plain weave.

Woven glass cloths are employed for various applications. One of theapplications for woven glass cloths includes printed circuit boards(PCBs). A printed circuit board (PCB) is a structure that mechanicallysupports and electrically connects electronic components usingconductive pathways formed on a non-conductive substrate. Dielectricsthat can be employed for the non-conductive substrates include, forexample, FR-4 (Woven glass and epoxy), FR-5 (Woven glass and epoxy),G-10 (Woven glass and epoxy), CEM-3 (Woven glass and epoxy), CEM-4(Woven glass and epoxy), and CEM-5 (Woven glass and polyester). Theconductive pathways are typically formed with copper. The board withcopper on it is called a “copper-clad laminate.”

Conductive anodic filament (CAF) failure is an electrochemical failureof electronic substrates involving growth of a metal-containing filamentsubsurface along the polymer-glass interface, from anode to cathode. CAFfailures are increasing as circuit density increases on printed circuitboards. Several conditions must be present in order for CAF formation toensue. Foremost among those is a pathway between adjacent plated throughholes (PTHs) of different voltages. This pathway is a result ofinterfacial delamination of the resin from the glass cloth or improperglass surface coverage during fabrication.

Glass cloth manufacturing processes known in the art leave anappreciable amount of organic residue on the glass surface. The organicresidue subsequently interferes with the bonding between a couplingagent and the glass cloth surface containing silanols. This in turnresults in poor interfacial adhesion and provides the pathway necessaryfor CAF formation. Woven glass cloth is currently processed in aroll-to-roll format utilizing several elevated temperature bakingoperations to remove the sizing agent from the cloth. Unfortunately, notall of the sizing is removed. This appears to be by design as thetensile strength of the glass cloth decreases significantly followingelevated temperature exposure.

SUMMARY

A solvent wash employing a polar washing solvent is employed toeffectively remove the sizing agent on a woven glass cloth, whileretaining the tensile strength of the woven glass cloth. Loss of tensilestrength of the woven glass cloth due to removal of a sizing agent fromthe woven glass cloth is compensated by simultaneous or subsequentdeposition of a coupling agent on surfaces from which the sizing agentis removed. The concurrent removal of the sizing agent and deposition ofthe coupling agent provides an effective removal of the sizing agentwhile maintaining sufficient tensile strength to structurally supportthe woven glass cloth. Further, integration of the removal of the sizingagent and the simultaneous deposition of the coupling agent in thewashing solvent in a same processing step can provide a cost-effectivemanufacturing method for forming a finished woven glass cloth.

According to an aspect of the present disclosure, a method of treating awoven glass cloth is provided, which includes providing a solutionincluding at least a solvent and a coupling agent; removing a sizingagent from surfaces of the woven glass cloth in a bath including thesolution or another solution; and immersing the woven glass cloth in thesolution, wherein a compound that is derived from the coupling agent isdeposited on the surfaces of the woven glass cloth in the solution.

According to another aspect of the present disclosure, an apparatus fortreating a woven glass cloth includes: at least one container includingat least one solution, the at least one solution including acoupling-agent-including solution that includes a solvent and a couplingagent and having a chemistry that causes a compound that is derived fromthe coupling agent to be deposited on surfaces of a woven glass clothintroduced into the coupling-agent-including solution, the at least onesolution includes a sizing-agent-dissolving solution for removing asizing agent from the surfaces of the woven glass cloth, wherein thesizing-agent-dissolving solution is the same as, or different from, thecoupling-agent-including solution; and means for immersing the wovenglass cloth in, and for subsequently removing the woven glass cloth outof, the coupling-agent-including solution.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a plot of an extension distance versus load on first threecomparative exemplary samples of a woven glass cloth that includes asizing agent and not including a coupling agent.

FIG. 2 is a plot of an extension distance versus load on second threecomparative exemplary samples of a woven glass cloth that wereoriginally the same as the woven glass cloth of the first threecomparative exemplary samples of FIG. 1, and were subsequently subjectedto caramelization and heat clean.

FIG. 3 is a plot of an extension distance versus load on two samples ofa woven glass that were originally the same as the woven glass cloth ofthe first three comparative exemplary samples of FIG. 1, and weresubsequently subjected to a treatment by a washing solution includingacetone and a coupling agent according to an embodiment of the presentdisclosure.

FIG. 4 is a schematic vertical cross-sectional view of a first exemplaryapparatus for treating a roll of a woven glass cloth according to anembodiment of the present disclosure.

FIG. 5 is a schematic vertical cross-sectional view of a secondexemplary apparatus for treating a roll of a woven glass cloth accordingto an embodiment of the present disclosure.

FIG. 6 is a schematic vertical cross-sectional view of a third exemplaryapparatus for treating a roll of a woven glass cloth according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

As stated above, the present disclosure relates to a manufacturingprocess to clean a woven glass cloth, which is now described in detail.

As used herein, a “sizing agent” or an “organic sizing” refers to amaterial that is at least temporarily incorporated into glass fibersstanding alone or woven glass fibers to act as filler or glaze toprovide structural support. Starch and starch-derivatives are typicallyemployed as a sizing agent for a woven glass cloth.

As used herein, a “binding polymer material” refers to a polymermaterial that becomes embedded in a woven glass cloth and providesstructural support to the glass fibers of the woven glass cloth.

As used herein, a “coupling agent” refers to a material that provides apermanent bond between glass fibers in a woven glass cloth and a bindingpolymer material.

As used herein, “coupling” of a woven glass cloth refers to a process ofproviding bonding between glass fibers in a woven glass and a bindingpolymer material.

A woven glass cloth that includes a sizing agent therein is provided. Atthis step, the sizing agent is in the same form and concentration asoriginally applied to glass fibers prior to weaving of the glass fibers.Thus, the woven glass cloth is not caramelized or heat treated at thisstep.

The woven glass cloth can be provided by weaving multiple glass fibersoriented in at least two different directions. As provided, the multipleglass fibers in the woven glass cloth have a coating of a sizing agentthereupon. Further, the woven glass cloth is not embedded in a matrixresin or any other binding polymer material as provided.

A woven glass cloth can be provided in any manner. A series ofprocessing steps can be employed to convert molten glass into a wovenglass cloth. An exemplary series of processing steps includes, forexample, an extraction step, a warping step, a slashing step, anentering step, and a weaving step. For example, glass fibers can beextracted from molten glass through a set of holes in the bushingcontaining the molten glass. Water can be sprayed to cool the glassfibers during extraction before the glass fibers are rubbed against asurface containing a sizing agent. The sizing agent can be starch basedas known in the art. The contact between the glass fibers and thesurface containing the sizing agent is typically performed at atemperature lower than 100° C., and the duration of contact between theglass fibers and the surface containing the sizing agent can be lessthan 0.5 milliseconds for any point on the glass fibers. The surfacecontaining the sizing agent can be provided by a roller including thesizing agent. The fiber glasses are pulled through past the surfacecontaining the sizing agent at a pull rate, which can be greater than1,000 m/min to form bobbins.

In the warping step, multiple bobbins of the glass fiber are pulledsimultaneously to form a section beam, in which multiple glass fibersare aligned along the direction of the pull. Several section beams canbe consolidated into a set.

In the slashing step, warp ends of the set's multiple section beams arecombined into a single beam for weaving, which is called a warp or aloom beam. An additional sizing agent can be applied to a threadsheetduring slashing. The additional sizing agent penetrates and encapsulatesindividual warp ends so as to minimize broken filaments and to avoidabrasion of individual strands. The organic sizing applied at theslashing step, i.e., the additional sizing agent, facilitates thesubsequent steps of entering and weaving.

In the entering step, a warp is set up for installation in a loom. Awarp can contain over 4,500 individual ends depending on the design andthe style of the warp. Each warp end is drawn through a drop wire,heddles, and a reed, either by machine or hand. The drop wire, theheddles, and the reed work together to mechanically arrange and controla warp yarn spreadsheet on the loom during the entering step.

In the weaving step, a warp beam is installed in the loom. The fillingyarns are interlaced at a 90 degree angle to the warp ends on the loom.Rapier technology or air jet technology can be employed to interlace thefilling yarns. The interlaced fabric is called a greige or a loom state.The interlaced fabric is then wound on a roll, and the weaving step iscomplete. The interlaced fabric, either on a roll or as a cut-up piece,is a woven glass cloth that can be employed for subsequent processes ofthe present disclosure.

Once a woven glass cloth is provided, the woven glass cloth is treatedin order to remove at least a substantial portion of the sizing agentand to deposit a coupling agent thereupon.

In a comparative exemplary processing scheme, a glass clothmanufacturing process can utilize several elevated temperature bakes to“clean” the glass cloth prior to deposition of a coupling agent. Duringthe cleaning of the glass cloth, the sizing agent, which is appliedduring extraction of the glass fibers and/or the slashing step, is atleast partially removed to expose at least some surfaces of the glassfibers in preparation for subsequent deposition of the coupling agent.However, as the sizing agent is removed during the exposure to elevatedtemperature performed to clean the glass cloth, the tensile strength ofthe glass cloth decreases dramatically. In some cases, the decrease inthe tensile strength of the glass cloth due to exposure to elevatedtemperature can be by more than 50% of the original tensile strength ofthe glass cloth before cleaning. A decrease in the tensile strength byalmost an order of magnitude has also been observed.

Since the glass cloth is processed in a roll-to-roll format forsubsequent application of a coupling agent and a binding polymermaterial, adequate tensile strength is required to pull the cloth from afeed reel to a take up reel. In order to provide sufficient tensilestrength to a woven glass cloth after the cleaning process, thetemperature and the duration of the elevated temperature bakes areselected so that less than 100% of the sizing agent is removed in theelevated temperature bakes. A significant fraction, estimated to be morethan 50% of the amount originally present in a newly woven glass cloth,of the sizing agent is present after the cleaning step. Since the sizingagent is starch-based, an organic residual material, or residual organic“contamination” material is present in the woven glass cloth aftercleaning. From the perspective of mechanical strength, a low level ofresidual organic contamination enhances the tensile strength of thecleaned woven glass cloth. However, the residual organic contaminationmaterial is detrimental to the effectiveness of subsequent deposition ofa coupling agent because a significant fraction of the surfaces of theglass fibers is covered by the residual organic contamination material,and the coupling agent cannot directly bond to the surfaces of the glassfibers wherever the residual organic contamination material is present.

The elevated temperature bakes can be effected, for example, by a seriesof processing steps that include a caramelization step and a heatcleaning step.

The caramelization step is a continuous heat treatment process designedto remove a significant portion of the sizing agent. During thecaramelization step, a sheet of a woven glass cloth is continuouslymoved through a caramelizer or a coronizer. The caramelizer and thecoronizer provide a high temperature process that oxidizes a significantportion of the sizing agent and any additional organic binders from thewoven glass cloth, which is in the form of a greige or a loom state.

The caramelization step is followed by the heat cleaning step, duringwhich the woven glass cloth in the form of the greige or the loom stateis wound onto mandrels then subjected to another elevated temperaturebake to drive off an additional amount of the sizing agent from thewoven glass cloth. The mandrels are first placed on racks, and thenloaded into a large oven, and then exposed to an elevated temperature toremove additional amount of the sizing agent and additional organicbinders.

Once the woven glass cloth is cleaned employing the caramelization stepand the heat cleaning step, a finishing step is performed to apply acoupling agent to the woven glass cloth. In one embodiment, thefinishing step can be performed in an acidic bath having a pH from 4.0to 5.0. A silicon-containing coupling agent can be subjected topre-hydrolysis in a solvent prior to application to the woven glasscloth, for example, by immersion in the acidic bath.

For example, Dow Corning® Z-6032 Silane, which is a benzylamine couplingagent that is commercially available from Dow Corning®, may be appliedto form dilute aqueous dispersions including 0.1% to 1.0% of activesilicon-containing coupling agent by weight. Most silicious surfaces canbe treated directly by first diluting one part of the silicon-includingcoupling agent with four parts of an ether alcohol solvent, such aspropylene glycol methyl ether (PGME), and by blending in a high shearmixer. The coated woven glass cloth can be subsequently heated topromote condensation thereupon.

In an exemplary processing scheme according to an embodiment of thepresent disclosure, the set of steps including the caramelization step,the heat cleaning step, and the finishing step is replaced with a singlewet processing step employing a solvent wash. The solvent wash can beperformed in a wet bath. The solvent wash effectively removes the sizingagent while retaining the tensile strength. Moreover, a coupling agentis deposited simultaneously with the removal of the sizing agent. Thiscan also be completed using subsequent baths, one to remove sizing and asecond to deposit coupling agent.

The solution of the bath includes a non-aqueous solution including apolar solvent and a coupling agent. Thus, the solution is notwater-based. The woven glass cloth is immersed in the solution, andremoval of the sizing agent and deposition of a compound that is derivedfrom the coupling agent occur simultaneously on the woven glass that isimmersed in the solution.

In one embodiment, the coupling agent can have a formula of:

in which R represents an organofunctional group that can subsequentlybind to a polymer, k is a positive integer, and each of X1, X2, and X3represents a hydrolysable group that can be the same or different amongthemselves.

In another embodiment, the coupling agent can have a formula of:

in which R represents an organofunctional group that can subsequentlybind to a polymer, k is a positive integer, l is another positiveinteger that is independent of k, and each of X1, X2, X3, Y1, Y2, and Y3represents a hydrolysable group that can be the same or different amongthemselves.

In yet another embodiment, the coupling agent can have a formula of:

in which R represents an organofunctional group that can subsequentlybind to a polymer, k is a positive integer, l is another positiveinteger that is independent of k, m is yet another integer that isindependent of k and l, and each of X1, X2, X3, Y1, Y2, Y3, Z1, Z2, andZ3 represents a hydrolysable group that can be the same or differentamong themselves.

In one embodiment, the coupling agent includes a silicon atom and atleast one hydrolysable group directly attached to the silicon atom. Eachof the at least one hydrolysable group can include a hydrolysable grouphaving a formula of OC_(p)H_(2p+1), in which p is any positive integer.For example, each of the at least one hydrolysable group can beindependently selected from OCH₃, OC₂H₅, and OC₃H₇.

In one embodiment, the coupling agent includes three hydrolysable groupsthat are attached to a silicon atom and having a formula ofOC_(p)H_(2p+1), OC_(q)H_(2q+1), and OC_(r)H_(2r+1), respectively,wherein p, q, and r are independent positive integers.

The coupling agent also includes an organofunctional group that forms abond with a polymer in a subsequent processing step in which a bindingpolymer material is applied.

Upon dissolving in the non-aqueous solution containing a hydrolysiscatalyst, the coupling agent is hydrolyzed. A derivative of the couplingagent is thereby formed in the non-aqueous solution. The chemicalformula for the derivative of the coupling agent can be

in which R represents an organofunctional group that can subsequentlybind to a polymer, k is a positive integer, or can be

in which R represents an organofunctional group that can subsequentlybind to a polymer, k is a positive integer, l is another positiveinteger that is independent of k, or can be

in which R represents an organofunctional group that can subsequentlybind to a polymer, k is a positive integer, l is another positiveinteger that is independent of k, m is yet another integer that isindependent of k and l.

The hydroxide groups in the hydrolyzed derivative of the coupling agentinteract with dangling hydroxide groups that are bonded to silicon atomson the surface of the glass fibers in the woven glass cloth. A watermolecule can be formed from two hydroxide groups that come into contactwith each other, thereby forming a —Si—O—Si— bond. Thus, a compound thatis derived from the coupling agent by hydrolyzation and dehydration isbonded to the silicon atoms in the glass fibers in the woven glasscloth.

The polar solvent is a liquid that dissolves the sizing agent, which isan organic material. Polar solvents that can dissolve the sizing agentinclude acetone, tetrahydrofuran (THF), ethyl acetate, ethanol, andmethanol. Non-polar solvents that can dissolve the sizing agent and beused for the purposes of the present disclosure include toluene. Therange of the Hildebrand solubility parameter for suitable polar solventsfor dissolving the sizing agent is from, and including, 17.4 MPa^(0.5)and to, and including, 21.7 MPa^(0.5). It is noted that the Hildebrandsolubility parameters for ethanol and methanol are outside this range.

In one embodiment, the polar solvent is not only effective at removingthe sizing, but also dissolves the coupling agent. Exemplary polarsolvents that provide these dual functions include acetone,tetrahydrofuran (THF), and ethyl acetate.

In one embodiment, the solution can further include an acidic catalyst.The acidic catalyst can be, for example, acetic acid or formic acid.Further, additional catalysts conventionally employed in deposition of acoupling agent may also be added.

The exemplary processing scheme according to an embodiment of thepresent disclosure does not require any elevated temperature bake. Thus,the removal of the sizing agent does not need to employ an elevatedtemperature sufficient to remove the sizing agent by oxidation, i.e.,burning. In one embodiment, the temperature of the woven glass cloth canbe maintained below 100 degree Celsius between the weaving of themultiple glass fibers and the immersing of the woven glass cloth in thesolution. In another embodiment, the temperature of the woven glasscloth can be maintained between 50 degrees Celsius between the weavingof the multiple glass fibers and the immersing of the woven glass clothin the solution.

In one embodiment, the temperature of the bath including the polarsolvent and the coupling agent as dissolved therein can be between 0degrees Celsius and 100 degrees Celsius. In another embodiment, thetemperature of the bath including the polar solvent and the couplingagent as dissolved therein can be between 10 degrees Celsius and 50degrees Celsius.

Relative to the comparative exemplary processing scheme, the exemplaryprocessing scheme according to an embodiment of the present disclosureprovides a more thorough coating of the coupling agent, and can provideenhanced tensile strength in the woven glass cloth prior to applicationof a binding polymer material. The weight of the woven glass clothprocessed with the methods of the comparative exemplary processingscheme loses weight by less than 0.1% during the processing steps ofelevated temperature bakes. In contrast, a woven glass cloth treatedwith the solvent wash according to the exemplary processing schemeaccording to an embodiment of the present disclosure can lose weight bymore than 0.2% during the immersing in the solution.

As a theoretical matter, the weight percentage of a coupling agentapplied to a woven glass during the solvent wash can be estimated in thefollowing manner. The radius of a typical glass fiber, as determined bymeasuring the cross-sectional profile of glass fibers, is about 0.1 mil,or 2.54×10⁻⁴ cm. Thus, the volume of a glass fiber having a length of 1cm is about 2.03×10⁻⁷ cm³. Since the density of a glass fiber is about2.55 g/cm³, the mass of the glass fiber having a length of 1 cm is about5.17×10⁻⁷ g. 3-aminopropyl triethoxysilane (APS), which is a couplingagent employed in experiments that have led to the instant disclosure,forms a monolayer on the surface of glass fibers. The thickness of themonolayer of APS is about 0.9 nm, or 9×10⁻⁸ cm, which is less than1×10⁻⁷ cm. If a coating of APS on the fiber glass surfaces is assumed toinclude up to three monolayers of APS, the volume of a cylindrical shellof APS around the sidewall of a 1 cm long glass fiber is less than4.62×10⁻¹⁰ cm³. Since the density of APS is 0.949 g/cm³, the mass of thecylindrical shell of APS around the sidewall of the 1 cm long glassfiber is less than 4.38×10⁻¹⁰ g. Thus, if the cylindrical shell of APSaround the sidewall of the 1 cm long glass fiber is removed, the weightpercentage of the coupling agent on a glass fiber in general is on theorder of 100%×(4.38×10⁻¹⁰ g)/(5.17×10⁻⁷ g+4.38×10⁻¹⁰ g)=0.085%. Thus,the order of magnitude for the weight percentage of a coupling agent onglass fibers should normally be on the order of 0.1%.

The above calculations show that the order of magnitude for thefractional weight of the sizing agent on glass fibers should also be onthe order 0.1% if the amount of residual sizing agent on the glassfibers after preparation for application of a coupling agent (forexample, at the end of the elevated temperature bakes) is to bemaintained on par with the amount of the coupling agent to be applied.

In order to quantify the effectiveness in removal of the sizing agent inthe exemplary processing scheme according to an embodiment of thepresent disclosure, different groups of experimental samples wereprepared and measured in the course of experiments leading to thepresent disclosure. Specifically, a first group of experimental samplessampled immediately after the weaving step, i.e., before the elevatedtemperature bakes or the solvent wash. A second group of samples wereprepared by providing samples of the same material as the first group ofexperimental samples and subsequently employing the comparativeexemplary processing scheme thereupon in which elevated temperaturebakes are employed. The temperature and duration of the elevatedtemperature bake was 500° C. and 60 minutes, respectively, for thesecond group. A third group of experimental samples were prepared byproviding additional samples of the same material as the first group ofexperimental samples and subsequently employing the exemplary processingscheme thereupon according to an embodiment of the present disclosure.Acetone was employed as the solvent and APS was employed as the couplingagent for the third group. The duration of the solvent wash was 20minutes.

Weight loss was measured on each group. The method employed formeasuring the weight loss is an industry standard method based on ASTMD-4963-94, “Standard Test Method For Ignition Loss of Glass Strands andFabrics.” Specifically, experimental samples were pre-dried at 105° C.for 60 minutes to drive off water. The experimental samples were thencooled to ambient temperature in a dessicator to prevent condensation ofmoisture. Then, the experimental samples were placed in a muffle furnaceand baked at 625° C. for 30 minutes. By comparing the weightdistribution of the first group, the second group, and the third group,the average and the standard distribution of weight loss were calculatedfor each of the comparative exemplary processing scheme and theexemplary processing scheme according to an embodiment of the presentdisclosure.

The average of weight loss for the comparative exemplary processingscheme was 0.1140%. The standard deviation of weight loss for thecomparative exemplary processing scheme was 0.0555%. The average ofweight loss for the exemplary processing scheme according to anembodiment of the present disclosure was 0.3698%. The standard deviationof weight loss for the exemplary processing scheme according to anembodiment of the present disclosure was 0.0919%.

The above data indicates that the method, i.e., the solvent wash, of theexemplary processing scheme according to an embodiment of the presentdisclosure can be at least three times more effective in removing sizingagents than the method of the comparative exemplary processing scheme.Further, the data above also indicates that at least 0.25% of the totalweight of woven glass cloth prepared by employing elevated temperaturebakes according to the comparative exemplary processing scheme isattributable to a residual sizing agent that is not removed even afterthe elevated temperature bakes.

The mechanical strength of woven glass cloths was also measured for thethree groups of experimental samples. Table 1 below tabulates the resultof the mechanical strength measurements performed on the three groups ofexperimental samples.

TABLE 1 Table of data on mechanical strengths of woven glass clothsamples. Maximum Maximum Young's Load to break Tensile Strength tensilestrain Modulus (mean +/− (mean +/− (mean +/− (mean +/− standard dev.;standard dev.; standard dev.; standard dev.; Sample group unit: Newton)unit: MPa) unit: %) unit: MPa) First Group 79.96 +/− 4.61 141.46 +/−8.16  2.65 +/− 0.23 11,074 +/− 251 (after weaving) Second Group 23.84+/− 5.05 42.23 +/− 8.95 1.18 +/− 0.08  6,731 +/− 993 (after elevatedtemperature bake) Third Group  93.30 +/− 14.63 165.28 +/− 25.92 3.14 +/−1.16   10,173 +/− 1,392 (after solvent wash)

FIG. 1 is a plot of an extension distance versus load on first threecomparative exemplary samples representative of, and selected from, thefirst group, i.e., the group of experimental samples of a woven glasscloth that includes a sizing agent and not including a coupling agentand not subjected to any elevated temperature bake or a solvent wash.

FIG. 2 is a plot of an extension distance versus load on second threecomparative exemplary samples representative of, and selected from, thesecond group, i.e., the group of experimental samples of a woven glasscloth that were subjected to caramelization and heat clean.

FIG. 3 is a plot of an extension distance versus load on two samplesrepresentative of, and selected from, the third group, i.e., the groupof experimental samples for a woven glass that were subjected to atreatment by a washing solution including acetone and a coupling agentaccording to an embodiment of the present disclosure.

Load to break is measured from the experimental samples. Maximum tensilestress and maximum tensile strain are calculated at the extension (theincremental length in the stretched woven glass cloth relative to theoriginal length of the woven glass cloth) that supports the maximumload. The maximum tensile stress is calculated by dividing the load tobreak by the cross-sectional area of each sample. Young's modulus wascalculated from cursor-selected data points in the linear elastic regionin a plot of an extension distance versus load.

As can be seen in the data in Table 1 and FIGS. 1, 2, and 3, a solventwash can result in effective cleaning of the woven glass cloth whileretaining the tensile strength. Moreover, the coupling agent can bedeposited on the cleaned glass surface simultaneously. Acetone,tetrahydrofuran (THF), and ethyl acetate are effective solvents fordissolving a sizing agent. In general, a solvent having a Hildebrandsolubility parameter within a range from, and including, 14.7 MPa^(0.5)and to, and including, 24.7 MPa^(0.5) can be an effective solvent forremoving a sizing agent.

The exemplary processing scheme according to an embodiment of thepresent disclosure cleans the glass fibers in a woven glass cloth andsimultaneously deposits a silicon-including coupling agent on the glassfibers in the woven glass cloth. The exemplary processing schemeaccording to an embodiment of the present disclosure provides retentionof tensile strength of the woven glass cloth, which is not possible inthe comparative exemplary processing scheme that employs elevatedtemperature bakes (or any equivalent heat cleaning processes). Further,cleaner glass fiber surfaces with less residual sizing agent can beprovided by the exemplary processing scheme according to an embodimentof the present disclosure relative to the comparative exemplaryprocessing scheme that employs elevated temperature bakes. It is notedthat the more thorough the cleaning is in the comparative exemplaryprocessing scheme (for example, by increasing the temperature or theduration of the elevated temperature bakes), the more loss in a sizingagent occurs, and with the loss of the sizing agent, the tensilestrength of the woven glass cloth decreases rapidly. Yet further, theexemplary processing scheme according to an embodiment of the presentdisclosure replaces multiple processing steps (two extended bakingoperations and a separate coupling agent application step) in thecomparative exemplary processing scheme with a single solvent washingstep.

In an alternate exemplary processing scheme according to anotherembodiment of the present disclosure, the glass fibers in a woven glasscloth can be cleaned in a first bath including a first polar solvent,and subsequently a silicon-including coupling agent can be deposited onthe glass fibers in the woven glass cloth in a second bath including asecond polar solvent. In this embodiment, the woven glass cloth istreated sequentially in two baths, in a first bath to remove the sizingagent, and the second bath to deposit a coupling upon the glass fibersin the woven glass cloth.

The solution in the first bath, which is herein referred to as asizing-agent-dissolving solution, removes the sizing agent, and may, ormay not, include a coupling agent. The solution in the second bath,which is herein referred to as a coupling-agent-including solution,includes a coupling agent, and may, or may not, remove the sizing agent.Thus, the sizing-agent-dissolving solution does not need to be able todeposit a coupling agent, but dissolves the sizing agent. Suitable polarsolvents for the sizing-agent-dissolving solution include acetone,tetrahydrofuran (THF), and ethyl acetate. Suitable non-polar solventsfor the sizing-agent-dissolving solution include toluene.

The coupling-agent-including solution may, but does not need to,dissolve the sizing agent. The coupling-agent-including solutiondeposits a coupling agent to the glass fibers in the woven glass cloth.Suitable polar solvents for the coupling-agent-including solutioninclude acetone, tetrahydrofuran (THF), ethyl acetate, ethanol, andmethanol. Suitable non-polar solvents for the coupling-agent-includingsolution include toluene.

In one embodiment, the coupling-agent-including solution can furtherinclude an acidic catalyst. The acidic catalyst can be, for example,acetic acid or formic acid. Further, additional catalysts conventionallyemployed in deposition of a coupling agent may also be added.

In one embodiment, the first bath and the second bath are prepared astwo separate baths, and the woven glass cloth is sequentially immersedin the first bath, pulled out of the first bath, and then immersed inthe second bath. In another embodiment, the woven glass cloth can remainin a same bath apparatus, and the bath apparatus can be filled with theliquid of the first bath, and then the liquid of the first bath isreplaced with the liquid of the second bath. The replacement of theliquid of the first bath with the liquid of the second bath can beperformed, for example, by draining the liquid of the first bath andthen refilling the bath apparatus with the liquid of the second bath, bygradually adding the liquid of the second bath while draining the liquidof the second bath, or by adding a suitable additive such as thecoupling agent if the first polar liquid is the same as the second polarliquid.

Once the surfaces of the glass fibers in the woven glass cloth aretreated in the solvent washing step of the exemplary processing schemeaccording to an embodiment of the present disclosure, a binding polymermaterial is applied to the woven glass cloth. The woven glass cloth isembedded in the applied binding polymer material to provide a “finished”or “coupled” woven glass cloth, in which the voids between the glassfibers are filled with the binding polymer material. An organofunctionalgroup (such as the organofunctional group R in the exemplary couplingagents discussed above) forms a chemical bond with the binding polymermaterial. Exemplary binding polymer materials include, but are notlimited to, epoxy resin, phenolic resins, polyphenylene ether (PPO)resins, cyanate esters, cyanate ester/epoxy blends, PPO/epoxy blends,and vinyl-functionalized PPO resins.

Referring to FIG. 4, a first exemplary apparatus 100 for treating a rollof a woven glass cloth 40 according to an embodiment of the presentdisclosure includes a first container 10 including a first solution 112,a second container 20 including a second solution 122, and a thirdcontainer 30 including a third solution 132.

At least the first solution 112 is a sizing-agent-dissolving solutionfor removing a sizing agent from the surfaces of the roll of the wovenglass cloth 40. In one embodiment, the sizing-agent-dissolving solutionincludes a coupling agent so that removal of a sizing agent anddeposition of a coupling agent occur simultaneously in thesizing-agent-dissolving solution. In another embodiment, thesizing-agent-dissolving solution does not include a coupling agent sothat removal of a sizing agent occurs in the sizing-agent-dissolvingsolution, and deposition of a coupling agent does not occur in thesizing-agent-dissolving solution.

At least the third solution 132 is a coupling-agent-including solutionfor depositing a coupling agent on the surfaces of the roll of the wovenglass cloth 40. In one embodiment, the coupling-agent-including solutionincludes a solvent that removes a sizing agent so that removal of thesizing agent and deposition of the coupling agent occur simultaneouslyin the coupling-agent-including solution. In another embodiment, thecoupling-agent-including solution does not remove a sizing agent sothat, deposition of a coupling agent occurs in thecoupling-agent-including solution, and removal of a sizing agent doesnot occur in the coupling-agent-including solution.

Each coupling-agent-including solution may, or may not, be asizing-agent-dissolving solution Likewise, each sizing-agent-dissolvingsolution may, or may not, be a coupling-agent-including solution.

In one embodiment, each of the first solution 112, the second solution122, and the third solution 132 is both a sizing-agent-dissolvingsolution and a coupling-agent-including solution.

In another embodiment, the first solution 112, the second solution 122,and the third solution 132 are sizing-agent-dissolving solutions, thesecond solution 122 and the third solution 132 arecoupling-agent-including solutions, and the first solution 112 is not acoupling-agent-including solution.

In even another embodiment, the first solution 112, the second solution122, and the third solution 132 are sizing-agent-dissolving solutions,the third solution 132 is a coupling-agent-including solution, and thefirst solution 112 and the second solution 122 are notcoupling-agent-including solutions.

In yet another embodiment, the first solution 112 and the secondsolution 122 are sizing-agent-dissolving solutions, the third solution132 is not a sizing-agent-dissolving solution, and the first solution112, the second solution 122, and the third solution 132 arecoupling-agent-including solutions.

In a still another embodiment, the first solution 112 and the secondsolution 122 are sizing-agent-dissolving solutions, the third solution132 is not a sizing-agent-dissolving solution, and the first solution112 is not a coupling-agent-including solution, and the second solution122 and the third solution 132 are coupling-agent-including solutions.

In further another embodiment, the first solution 112 is asizing-agent-dissolving solution, the second solution 122 and the thirdsolution 132 are not sizing-agent-dissolving solutions, and the firstsolution 112, the second solution 122, and the third solution 132 arecoupling-agent-including solutions.

In yet further another embodiment, the first solution 112 is asizing-agent-dissolving solution, the second solution 122 and the thirdsolution 132 are not sizing-agent-dissolving solutions, and the firstsolution 112 is not a coupling-agent-including solution, and the secondsolution 122 and the third solution 132 are coupling-agent-includingsolutions.

As discussed above, non-limiting examples for a polar solvent for asizing-agent-dissolving solution include acetone, tetrahydrofuran (THF),and ethyl acetate, and non-limiting examples for a polar solvent for acoupling-agent-dissolving solution include acetone, tetrahydrofuran(THF), ethyl acetate, ethanol, and methanol.

Thus, the first exemplary apparatus 100 includes at least onecoupling-agent-including solution (which includes at least the firstsolution 112) that includes a polar solvent and a coupling agent andhaving a chemistry that causes a compound that is derived from thecoupling agent to be deposited on surfaces of a roll of woven glasscloth 40 introduced therein. Further, at least onesizing-agent-dissolving solution (which includes at least the thirdsolution 132) for removing a sizing agent from the surfaces of the rollof woven glass cloth 40 is provided as well. Each of the at least onesizing-agent-dissolving solution can be the same as, or different from,one of the at least one coupling-agent-including solution.

Further, means are provided for immersing the roll of woven glass cloth40 in, and for subsequently removing the roll of woven glass cloth 40out of, the at least one sizing-agent-dissolving solution and the atleast one coupling-agent-including solution. Such means may include afeed-in roller 5, in-solution rollers (9, 11, 19, 21, 29, 31),out-of-solution rollers (15, 25), and a pull-out roller 35, which turnin synchronization to continuously or intermittently move the roll ofwoven glass cloth 40 through the first exemplary apparatus. A chemicalsupply system 80 and a chemical pumping system 1 can be provided in thefirst exemplary apparatus 100 to supply, and/or to remove, chemicalsincluding at least one polar solvent for each of the first solution 112,the second solution 122, and the third solution 132.

In one embodiment, the means for immersing the roll of woven glass cloth40 in, and for subsequently removing the roll of woven glass cloth 40out of, the at least one sizing-agent-dissolving solution and the atleast one coupling-agent-including solution can be configured to movethe roll of woven glass cloth 40 into a sizing-agent-dissolvingsolution, then to move the roll of woven glass cloth 40 out of thesizing-agent-dissolving solution, then to move the roll of woven glasscloth 40 into a coupling-agent-including solution that is different fromthe sizing-agent-dissolving solution, and then to move the roll of wovenglass cloth out of the coupling-agent-including solution.

In a non-limiting exemplary implementation of the first exemplaryapparatus 100, fresh solvent and a coupling agent can be added to thethird solution 132 in the third container 20. The third solution 132 canoverflow into the second container 20 through a counter current solventflow indicated by an arrow with a label “CCSF.” The second solution 122can overflow into the first container 10 through a counter currentsolvent flow indicated by another arrow with another label “CCSF.” Thelevel of the first solution 112 is lower than the level of the secondsolution 122, and the level of the second solution 122 is lower than thelevel of the third solution 132. The first solution 112 and the secondsolution can be initially provided as solutions without any couplingagent therein. During operation, due to the counter current solventflow, i.e., spillage, of solutions from the third solution 132 to thesecond solution 122, and from the second solution 122 to the firstsolution 112, the concentration of the coupling agent is the greatest inthe third solution 132, and is the lowest in the first solution 112.

Initially, the first solution 112, the second solution 122, and thethird solution 132 can be sizing-agent-dissolving solutions and thethird solution 132 can be a coupling-agent-including solution. Duringoperation of the first exemplary apparatus 100, the first solution 112,the second solution 122, and the third solution 132 become mixedsolutions each of which is both a sizing-agent-dissolving solution andcoupling-agent-including solution. The third solution 132 is the mosteffective as a coupling-agent-including solution because of fresh supplyof the coupling agent, and the first solution is primarily employed forthe function of a sizing-agent-dissolving solution. Thus, the roll ofthe woven glass cloth 40 is predominantly solvent-cleaned in the firstsolution 112, and is predominantly treated with the coupling agent inthe third solution 132. Upon exiting the first exemplary apparatus 100,the roll of the woven glass cloth 40 is sent to a dryer (not shown) andwound onto a take up mandrel (not shown).

Referring to FIG. 5, a second exemplary apparatus 200 for treating aroll of a woven glass cloth according to an embodiment of the presentdisclosure can be derived from the first exemplary apparatus 100 byeliminating the second container 20 including the second solution 122.The third solution 132 can overflow into the first container 10 througha counter current solvent flow indicated by an arrow with a label“CCSF.”

Referring to FIG. 6, a third exemplary apparatus 300 for treating a rollof a woven glass cloth according to an embodiment of the presentdisclosure can be derived from the second exemplary apparatus 100 byeliminating the first container 10 including the first solution 112.

Instead of eliminating at least one container from the first exemplaryapparatus 100, at least one additional container including an additionalsolution can be added between the first container 10 and the thirdcontainer. Such embodiments are expressly contemplated herein.

While the disclosure has been described in terms of specificembodiments, it is evident in view of the foregoing description thatnumerous alternatives, modifications and variations will be apparent tothose skilled in the art. Accordingly, the disclosure is intended toencompass all such alternatives, modifications and variations which fallwithin the scope and spirit of the disclosure and the following claims.

1. A method of treating a woven glass cloth comprising: providing asolution comprising a solvent and a coupling agent; removing a sizingagent from surfaces of said woven glass cloth in a bath including saidsolution or another solution; and immersing said woven glass cloth insaid solution, wherein a compound that is derived from said couplingagent is deposited on said surfaces of said woven glass cloth in saidsolution.
 2. The method of claim 1, wherein said compound is derivedfrom said coupling agent and coupled to glass fibers of said woven glasscloth through at least one —Si—O—Si— bond.
 3. The method of claim 1,wherein said coupling agent comprises a silicon atom.
 4. The method ofclaim 3, wherein said coupling agent further comprises at least onehydrolysable group directly attached to said silicon atom.
 5. The methodof claim 4, wherein said at least one hydrolysable group includes ahydrolysable group having a formula of OC_(p)H_(2p+1), wherein p is apositive integer.
 6. The method of claim 5, wherein said at least onehydrolysable group is selected from OCH₃ and OC₂H₅.
 7. The method ofclaim 3, wherein said coupling agent includes three hydrolysable groupshaving a formula of OC_(p)H_(2p+1), OC_(q)H_(2q+1), and OC_(r)H_(2r+1),respectively, wherein p, q, and r are independent positive integers. 8.The method of claim 4, wherein said coupling agent further includes anorganofunctional group that forms a bond with a polymer.
 9. The methodof claim 1, further comprising applying a binding polymer material tosaid woven glass cloth after said immersing, wherein said woven glasscloth is embedded in said applied binding polymer material,
 10. Themethod of claim 1, wherein said woven glass cloth is provided by weavingmultiple glass fibers oriented in at least two different directions. 11.The method of claim 10, wherein temperature of said woven glass cloth ismaintained below 100 degree Celsius between said weaving of saidmultiple glass fibers and said immersing of said woven glass cloth insaid solution.
 12. The method of claim 1, wherein said solvent is apolar solvent that includes at least one of acetone, tetrahydrofuran(THF), ethyl acetate, ethanol, and methanol.
 13. The method of claim 1,wherein said woven glass cloth is not embedded in a matrix resin. 14.The method of claim 1, wherein said solution is not a water-basedsolution.
 15. The method of claim 1, wherein said compound is derivedfrom said coupling agent by hydrolyzation and dehydration upon couplingto surfaces of glass fibers in said woven glass cloth.
 16. The method ofclaim 1, wherein said removal of said sizing agent and said depositionof said compound occur concurrently on said woven glass in saidsolution.
 17. The method of claim 1, wherein said another solution is adifferent solution than said solution.
 18. The method of claim 1,wherein said compound is deposited on said surfaces of said woven glasscloth after said removing of said sizing agent from said surfaces ofsaid woven glass cloth.
 19. The method of claim 1, wherein said bathincludes said another solution, and said another solution includes asolvent that dissolves said sizing agent.
 20. An apparatus for treatinga woven glass cloth comprising: at least one container including atleast one solution, said at least one solution including acoupling-agent-including solution that comprises a solvent and acoupling agent and having a chemistry that causes a compound that isderived from said coupling agent to be deposited on surfaces of a wovenglass cloth introduced into said coupling-agent-including solution, saidat least one solution includes a sizing-agent-dissolving solution forremoving a sizing agent from said surfaces of said woven glass cloth,wherein said sizing-agent-dissolving solution is the same as, ordifferent from, said coupling-agent-including solution; and means forimmersing said woven glass cloth in, and for subsequently removing saidwoven glass cloth out of, said coupling-agent-including solution. 21.The apparatus of claim 20, wherein said sizing-agent-dissolving solutionis the same as said coupling-agent-including solution.
 22. The apparatusof claim 20, wherein said sizing-agent-dissolving solution is differentfrom said coupling-agent-including solution, and said means isconfigured to move said woven glass cloth into saidsizing-agent-dissolving solution, then to move said woven glass clothout of said sizing-agent-dissolving solution, then to move said wovenglass cloth into said coupling-agent-including solution, and then tomove said woven glass cloth out of said coupling-agent-includingsolution.
 23. The system of claim 20, wherein said coupling agentcomprises silicon and at least one hydrolysable group directly attachedto said silicon atom.
 24. The system of claim 23, wherein said at leastone hydrolysable group includes a hydrolysable group having a formula ofOC_(p)H_(2p+1), wherein p is a positive integer.
 25. The system of claim20, wherein said solvent is a polar solvent includes at least one ofacetone, tetrahydrofuran (THF), ethyl acetate, ethanol, and methanol.